Cerebral vasospasm following subarachnoid hemorrhage is a potentially lethal complication. Clinical data suggest that this syndrome, like migraine headache, is gender and age related. We have utilized the isolated basilar artery from rabbits treated to produce various hormonal states to demonstrate increased sensitivity to serotonin (but not norepinephrine or PGF2 alpha) during acute withdrawal of sex hormones. We seek to ascertain the conditions under which sex hormones can alter cerebral vasoreactivity in vitro. Specifically, the role of estrogen and/or progesterone treatment or withdrawal on the response of the isolated rabbit basilar artery and extracerebral vessels will be examined. The time course, potential reversibility, and role of the endothelium in vasoreactivity will be studied. An understanding of the pathophysiology of sex hormone modulation of vasospasm could identify patients at special risk and suggest new therapeutic options.